GOLD WIRE BONDABILITY OF ELECTROLESS GOLD PLATING USING DISULFITEAURATE COMPLEX

Generally, contact or terminal areas are coated with nickel as a barri er layer; subsequently, gold plating is performed to maintain reliabil ity of electrical interconnection. Treatment using dilute solutions of palladium ions have been applied to initiate electroless nickel plati ng on copper substrates because copper has no catalytic action for the oxidation of hypophosphite. However, trace amounts of palladium ions may remain on the unwanted areas and extraneous nickel deposits are of ten observed. We confirmed that nickel films without extraneous deposi ts can be formed using the activation solutions containing dimethyl am ine borane (DMAB). Bondability on the electrolessly deposited gold was greatly influenced by the phosphorus contents of the deposited nickel films as the underlayer. Bonding strength after electroless gold plat ing was increased with increasing phosphorus contents in the nickel fi lms. Stabilizers in the electroless gold plating also influenced the b onding strength. Baths containing cupferron or potassium nickel cyanid e as a stabilizer showed superior bondability. Gold deposits having st rong orientation with Au(220) and Au(311) indicated high bond strength .